Mutation of a KRAS gene can be related to malignant tumors, such as lung adenocarcinoma, mucinous adenoma, ductal carcinoma of the pancreas, and colorectal carcinoma. Recent observations indicate that elevated levels of the protein Glutathione S-transferase-π (GST-π) is associated with such KRAS mutations.
Without wishing to be bound by any one particular theory, it has been found that upon suppression of GST-π in cells, the level of the cell cycle-regulating protein p21 can be surprisingly elevated.
One of the functions of the cell cycle-regulating protein p21 is to inhibit apoptosis. For example, p21 may have the effect of protecting a cell from apoptosis induced by a chemotherapeutic agent, both in vitro and in vivo. See, e.g., Gartel and Tyner, 2002, Mol Cancer Ther., 2002, 1(8):639-49; Abbas and Dutta, 2009, Nat Rev Cancer., 2009, 9(6):400-14. p21 is encoded by CDKN1A gene and belongs to the CIP/KIP family. p21 can function to inhibit cell cycle progression at the G1 phase and the G2/M phase by binding a cyclin-CDK complex. For example, the p21 gene undergoes activation by p53, a tumor suppressor gene. Upon activation of p53 due to DNA damage, p53 activates p21 so that the cell cycle is arrested at the G1 phase and the G2/M phase.
GST-π is a member of the Glutathione S-transferase (IUBMB EC 2.5.1.18) family of six isoenzymes that play a role in detoxification by catalyzing the conjugation of hydrophobic and electrophilic compounds with reduced glutathione. The GST-π gene (GSTP1) is a polymorphic gene encoding active, functionally different GSTP1 variant proteins that are thought to function in xenobiotic metabolism. GSTP1 may play a role in susceptibility to cancer and is expressed abundantly in tumor cells. See, e.g., Aliya S. et al. Mol Cell Biochem., 2003 November; 253(1-2):319-327. Glutathione S-transferase-π is an enzyme that in humans is encoded by the GSTP1 gene. See, e.g., Bora P S, et al. (October 1991) J. Biol. Chem., 266 (25): 16774-16777. The GST-π isoenzyme has been shown to catalyze the conjugation of GSH with some alkylating anti-cancer agents, suggesting that over-expression of GST-π would result in tumor cell resistance.
Elevated serum GST-π levels were observed in patients with various gastrointestinal malignancies including gastric, esophageal, colonic, pancreatic, hepatocellular, and biliary tract cancers. Over 80% of patients with Stage III or IV gastric cancer and even about 50% of those with Stage I and II had elevated levels of serum GST-π. See, e.g., Niitsu Y, et al. Cancer, 1989 Jan. 15; 63(2):317-23. GST-π was found to be a useful marker for predicting the recurrence of tumors in patients with oral cancer after chemotherapy. See, e.g., Hirata S. et al. Cancer, 1992 Nov. 15:70(10):2381-7.
In human colorectal cancer, KRAS mutation appears to induce overexpression of GST-π via activation of AP-1. See, e.g., Miyanishi et al., Gastroenterology, 2001; 121 (4):865-74.
Expression of GST-π increases in various cancer cells, which may be related to resistance to some anticancer agents. See, e.g. Ban et al., Cancer Res., 1996, 56(15):3577-82; Nakajima et al., J Pharmacol Exp Ther., 2003, 306(3):861-9.
Agents for suppressing GST-π have been disclosed for inducing apoptosis in cells. However, such compositions and techniques also caused autophagy and required the combined action of various agents. See, e.g., US 2014/0315975 A1. Moreover, suppressing GST-π has not been found to shrink or reduce tumors. For example, in a cancer that was overexpressing GST-π, the weights of tumors were not affected by suppressing GST-π, although other effects were observed. See, e.g., Hokaiwado et al., Carcinogenesis, 2008, 29(6):1134-1138.
There is an urgent need for methods and compositions to develop therapies for patients with malignancies, such as siRNA sequences, compounds and structures for inhibition of expression of GST-π and p21.
What is needed are methods and compositions for preventing or treating malignant tumors. There is a continuing need for RNAi molecules, and other structures and compositions for preventing, treating, or reducing malignant tumors.